A transmission is often provided in a drive train of a vehicle or other machine so that a drive ratio between input and output can be varied over an operating range of a prime mover. Accordingly, the prime mover can be operated over its operating torque and speed range while permitting the output to vary over different and usually considerably broader torque and speed ranges. Manual transmissions were developed to manually select one of several discrete transmission ratios. For example, a derailleur system in a bicycle or a conventionally geared transmission in an automobile implement various sprockets or gears that are alternatively engaged in order to select from a limited number of available gear ratios.
A variety of automatic transmissions have been developed to aid the vehicle or machine operator, wherein the appropriate transmission ratios for given conditions are automatically determined and implemented. For example, a conventional vehicle automatic transmission typically provides an automation of shifting between discrete gear engagements of the transmission using speed or torque sensing devices. Other transmissions use belt and pulley systems which vary the effective pulley diameter. Still other automatic transmissions utilize hydraulic systems comprising hydraulic pumps, motors and various valve arrangements. Such conventional automatic transmission systems are often complicated, heavy, and bulky, and therefore expensive. Further, such systems often shift abruptly in a stepped manner between discrete ratios, rather than in a smooth and continuous manner.